Gen 1, 2 and 3 all feel distinct enough to feel like unique and great experiences on their own. Gen 1 because it's the original, Gen 2 because it's built as a logical extension of Gen 1 and Gen 3 because it's a whole new directorial take on the series that would introduce a lot of tropes and mainstays with a wholly exotic region.

Gen 4 is when Masuda started to rip himself off and just remade Gen 3 but worse in almost every way. Gen 5 is when the series tried to recapture the Gen 1 magic but failed and all the intrusive elements of Gen 3 started to become actually troublesome.

In essence, gens 1-3 are soul and Gen 4 and beyond are pale imitations. This does not mean Gen 4 and 5 are bad games necessarily but they clearly lack the same kind of charm, passion, innovation and creativity of past gens.